The EGFR C797S Mutation Confers Resistance to a Novel EGFR Inhibitor CLN-081 to EGFR Exon 20 Insertion Mutations.

Introduction: EGFR exon 20 insertion mutations account for 5% to 10% of EGFR-mutated NSCLC. CLN-081 (formerly known as TAS6417), a novel covalent EGFR tyrosine kinase inhibitor, exhibits pan-mutation selective efficacy, including exon 20 insertions, in the clinical setting. Nevertheless, some patients may not respond to CLN-081 and resistance to CLN-081 may emerge over time in others. Methods: We exposed Ba/F3 cells transduced with EGFR exon 20 insertions (Y764_V765 insHH or A767_S768insSVD) to increasing concentrations of CLN-081 to generate resistant cells and then subjected their complementary DNA to sequencing to identify acquired mutations. We then evaluated effects of small molecules on engineered Ba/F3 cells on the basis of proliferation assays, Western blotting, and xenograft models. Results: All CLN-081 resistant clones harbored the EGFR C797S mutation. Ba/F3 cells with C797S (Ba/F3-C797S) were resistant to EGFR tyrosine kinase inhibitors targeting EGFR exon 20 insertion mutations, including CLN-081. Pimitespib, a selective heat shock protein 90 inhibitor, induced apoptosis in Ba/F3-C797S cells in vitro and inhibited growth of Ba/F3-C797S tumors in vivo. Ba/F3 cells with A763_Y764insFQEA-C797S remained sensitive to erlotinib. Conclusions: We conclude that the EGFR C797S mutation confers resistance to CLN-081. Our preclinical data suggest a potential small molecule to overcome CLN-081 resistance, which may benefit patients with lung cancer with EGFR exon 20 insertions.